I am about to get my XP100 rebarreled to 30BR. What do I need to instruct a very experienced gunsmith / barrel maker who is top of his game in making very accurate match rifles? Not sure they do many cast bullet exclusive ones. Want this barrel to shoot the RCBS 165gr bullet. Leade? Throat-length? What else?
Kind regards,
Peter.
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For the RCBS 165. 14 twist. .310 x 1 1/2 deg. included throat. Maybe .309 x 1 1/2 deg incl. if using something besides lino because my experience with RCBS moulds is they cast small in WWs. As far as the ball seat length? Seat the bullet where you like it and have the smith cut it to that length. Neck clearance? I always used .002 clearance but then again I never won many matches or set many records. My understanding is the best way to do it for accuracy is with a slight interference fit.
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I'd go 12' twist; It allows the use of most of the common molds if you change your mind about the boolit, and any advantage in a slower twist either in terms of accuracy or higher velocity actually achieved is likely negligible. Grouch
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Peter, + 1 on the 1-12 twist. as stated, this should stabilize any heavier bullet you might want to use. Another point mentioned was that RCBS molds are known for casting slightly smaller bullets that other molds, So, What I would do is take several sized bullets, plus a few that are loaded in un-primed cases to your desired seating depth to your gun smith and instruct him to cut the chamber so that when you chamber a round the front driving band is a tight fit in the throat and that the nose is engraved in the rifling. The draw back to this is, once chambered you will probably have to fire it, and should you want to use a heavier bullet like the RCBS 200 Sil. or a 311299,these will require the bullets being seated below the case neck, or a nose sizing die to make the heavier bullets ride the bore instead of engraving the rifling .
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I also vote for the 14 twist. I've used that twist in my Douglas barreled Hoch for the last 25+ years. It will stablize a 1.160 long PB bullet at 1400 fps and a 1.230 long GC bullet at 2000 fps. All my bullets are spitzers shot breech seated but, that doesn't effect stablization.
12 is ok but, you really don't need it. I just bought a RSK gain twist barrel, ending in 13 twist but, haven't mounted it it yet. I got that twist because I want to shoot 1.300 bullets at 1400 fps. We will see how that works this spring/summer.
Frank
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Thanks Guys for the input. Just to complicate things he offers different barrell diameters; 30 Tight (.3066” - .3075")in 12,13 &14 twist 30 cal (.3077 - .3080)in 8, 10 & 12 twist. So effectively I can also specify the diameter I want?? Do I want “Tight” or just go with the .3080?? regards,
Peter
Check out their web-site “truflite barrels” New Zealand. He will cut me two 15” barrels for the advertised pricing. I will go with the Premium grage although I am sure the Sporter Grade would be OK for IHMSA use.
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I like to shoot bullets as cast and just install the GC size for size or .001 larger. The tight barrel will limit you over all. If you got a .3075, it wouldn't be to bad as all the RCBS's I have cast close to .309 but, I would stay far away from a .3066.
Frank
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Thanks Guys for the input.
Just to complicate things he offers different barrell diameters;
30 Tight (.3066” - .3075")in 12,13 &14 twist
30 cal (.3077 - .3080)in 8, 10 & 12 twist.
So effectively I can also specify the diameter I want?? Do I want “Tight” or just go with the .3080??
regards,
Peter
Check out their web-site “truflite barrels” New Zealand. He will cut me two 15” barrels for the advertised pricing. I will go with the Premium grage although I am sure the Sporter Grade would be OK for IHMSA use.
Peter, you are talking about groove diameter. I would be more concerned about bore diameter since the 165 gr. RCBS is a bore-ride bullet and usually casts barely .300” on the bore-ride nose. I'd go for a .299” .2995” bore and a .308” groove diameter. You may have a tight engraving on the nose of the cb, but the lands will wear down after shooting a few matches.......Dan
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. All my bullets are spitzers shot breech seated but, that doesn't effect stablization.
Frank
Frank, I feel that is not all that true, not for sake of arguing, but to make my point; there is a difference between a 'breech-seated' cb compared to a 'fixed-ammo' cb. The breech-seated cb inherently has a practically 0% of cant to the bore at ignition, thus leaving the muzzle practically in perfect stability, no yaw.
On the other hand an ammo-loaded cb is almost impossible to launch from the throat without any cant with a result of a small percentage of yaw already at the muzzle, say maybe 1.5% to 2%.
Say both loads have the same 200yd down-range performance of a 2% loss in stability (yaw), the breech-seated cb will may still be in a stabilizing ability where the fixed-ammo cb would compound to a larger yaw of maybe 4%-5%, thus falling off the stability factor of bullet-length verses twist-rate formula.
I conclude this idea not from your statement, but from shooting shoulder-to-shoulder for 10 years in CBA matches against two very good Schuzten shooters. This the only explanation I can come up with because I can't get my Pro Class loads to perform as well as the Schuzten performance, percentage wise by percentage.
I would always play it safe calculating twist rate for a fixed-ammo load combination to go one step faster than calculated on paper, considering the inherit yaw of the fixed-ammo. Once a slower-rate twist barrel is made and it fails, there is no recourse except to go with a shorter/lighter bullet, or re-barrel.........Dan
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In my 30 PPC XP-100, the twist was 1:12 and it likes 180-grain bullets. Using Lapua brass I had the smith make the ID of the neck 0.332". With the bullet sized at 0.311” the Lapua necks were thinned to end up with 0.0005” per side of clearance or 0.001” overall. So the necks were reduced to 0.010” thickness. .311 + .010” + 0.10” = 0.331".
This was re-barreld late last year with an “overly expensive” Adams and Bennett 1:10 twist barrel from Midway for a .30 Silhouette (223 case necked-up). Still hunting for a decent load.
Tom
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. All my bullets are spitzers shot breech seated but, that doesn't effect stablization.
Frank
Frank, I feel that is not all that true, not for sake of arguing, but to make my point; there is a difference between a 'breech-seated' cb compared to a 'fixed-ammo' cb. The breech-seated cb inherently has a practically 0% of cant to the bore at ignition, thus leaving the muzzle practically in perfect stability, no yaw.
On the other hand an ammo-loaded cb is almost impossible to launch from the throat without any cant with a result of a small percentage of yaw already at the muzzle, say maybe 1.5% to 2%.
Say both loads have the same 200yd down-range performance of a 2% loss in stability (yaw), the breech-seated cb will may still be in a stabilizing ability where the fixed-ammo cb would compound to a larger yaw of maybe 4%-5%, thus falling off the stability factor of bullet-length verses twist-rate formula.
I conclude this idea not from your statement, but from shooting shoulder-to-shoulder for 10 years in CBA matches against two very good Schuzten shooters. This the only explanation I can come up with because I can't get my Pro Class loads to perform as well as the Schuzten performance, percentage wise by percentage.
I would always play it safe calculating twist rate for a fixed-ammo load combination to go one step faster than calculated on paper, considering the inherit yaw of the fixed-ammo. Once a slower-rate twist barrel is made and it fails, there is no recourse except to go with a shorter/lighter bullet, or re-barrel.........Dan
Are you saying that the reason that your production class rifle isn't as accurate as a SS target rifle is because of the twist? there is lots more to it than that.
If the bullet doesn't leave the barrel straight, there isn't anything you can do to make it competitive. If the bullet does't leave the barrel stablized, there is nothing you can do about that either. Well chambered Heavy and UnR rifles will not be effected by what your saying, either. Most production rifles are way over stabilized (twist wise) to start with and by that should win matches against target rifles?
What are you seeing at the target that tells you that? Tipped bullets? If it's tipped bullets, velocity can effect that as well as the bullet going through the transonic range.
The rifle this guy is building will come with a match type chamber and throat and a 12 twist will be way over stabilized for the 165 RCBS. If you look in the CBA match results, you'll see guys shooting a 200 gr bullet with a 13 twist in the Heavy & UnR classes. Those two classes are competive with the PB schuetzen rifles.
Frank
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